The present invention is directed to an improvement in tire treading or retreading matrices which include heating elements encased in a casting of aluminum or like metal in the manner disclosed in U.S. Pat. No. 3,088,171 issued May 7, 1963.
It has been noted that when heating elements (electrical or steam) are encased in molten material poured in a channel of a matrix, subsequent use causes failure of the heating elements because the terminal ends thereof do not have sufficient clearance within which to compensate for differences in expansion and/or contraction. In other words, when a heating element which is totally encased in a solid casting expands or contracts, any difference in relative expansion or contraction between the heating element and its casing relative to the material in which it is encased and the matrix which it surrounds will at times cause failure as, for example, by breaking the connection between the electrical coil and the connecting pin of the heating element (CALROD) likewise, such stresses caused during expansion and contraction while the matrix is in use could cause a steam coil to crack of separate from its fittings. In either case past efforts of correcting this problem, including those set forth in the latter-noted patent, proved unsatisfactory both from the standpoint of manufacturing which was a relatively difficult and time consuming operation and while in use.
In keeping with the foregoing, it is a primary object of the present invention to avoid the latter-noted and other disadvantages in both the manufacture and operation of heating devices which though specifically directed to matrices for prior treading or retreading operations are equally applicable as any type of a heating device in which a heating element, be it electrical, steam or the like, is encased in a body which is subject to expansion and/or contraction.
Another object of this invention is to provide a novel heating device specifically including a body having a continuous unending channel therein in which is disposed a heating element encased in a solid casting and means for traversing the channel and separating the solid material encasing opposite end portions of the heating elements whereby the latter are free to move relative to each other upon expansion and/or contraction of the heating elements, the material encasing the same and/or the body.
A further object of this invention is to provide a novel heating device of the type heretofore set forth wherein the traversing means is a spacer.
Another object of this invention is to provide a novel heating device of the type heretofore set forth wherein the end portions of the heating element are in lapping relationship and the transversing means is a spacer disposed between the lapping end portions of the heating element.